PURPOSE: To remove a micro-projection well from the surface of a cathode by specifying the pulse width of pulse voltage applied between an anode and a cathode.

CONSTITUTION: First of all, a high frequency of 17.5kHz/sec. is used as a power supply 1, boostered via a step-up transformer 2 and rectified via a diode 3. The positive side of high voltage is connected with the anode 5 of a cathode ray tube 4 and the negative side is connected with a heater 6, a cathode 7 and each electrode of the first 8, second 9 and third grid electrodes 10. Thereafter, the primary side voltage of the step-up transformer 2 is raised and pulse voltage having a pulse width of 10-7 to 10-4 sec. is applied between the anode 5 and the cathode 7, thereby processing high voltage. In this case, a high frequency ranging over 10kHz/sec to 10MHz/sec can also be used as a high frequency power supply.